Described below is a method for operating an electric or hybrid vehicle with shiftable transmission, in which at least one electric motor is employed for propelling the vehicle. Upon reaching a shift threshold, a shift operation is performed in the transmission of the vehicle. Herein, a value specifying the shift threshold is varied depending on at least one parameter. Also described below is a vehicle with at least one electric motor formed for propelling the vehicle.
DE 44 38 914 A1 describes an electric vehicle having an electric motor for propelling the vehicle as well as a transmission controller for controlling a gear change of an automatically shiftable transmission. For shifting optimum in terms of consumption, three different methods of a gear selection function are provided. In a first method, shift lines optimum in terms of consumption are stored in the transmission controller. These optimum shift lines consider losses in the partial systems of battery, power actuator, electric motor, transmission and auxiliary load. In the second variant, temporally non-constant influencing parameters on the losses are considered by adaptation of the optimum shift lines. Variables considered in adaptation of the shift lines optimum in terms of consumption include the transmission temperature, the temperature of the electric motor, the state of charge, the open-circuit voltage and the internal resistance of the battery. In order to consider these influences, calculations are performed. Correction factors are introduced into corresponding equations for the parameter adaptation.
Such an adaptation with correction factors for considering a larger number of influencing parameters is comparatively expensive.
Furthermore, in today's power trains of electric vehicles and hybrid vehicles with automatic transmission, the gear selection is effected according to shift maps. The input parameters of such shift maps include the driver's wish, thus the accelerator position, and the currently applied speed among other things. Upon full-load acceleration with the electric vehicle or hybrid vehicle, a shift operation occurs upon reaching a shift threshold, for instance a shift speed stored in the shift map. After performing the shift operation, a new subsequent speed appears in the power train. It results from the respective gear ratio variation. Usually, the static shift speed is set such that upon full-load acceleration that speed of the electric motor is reached, at which the nominal maximum power of the electric motor is achieved.